1. Field of the Invention
The present invention relates to a non-invasive method and apparatus for measuring differential blood flow between extremities for diagnosing cardiovascular conditions. In particular, the present invention relates to use of a pair of colorimeters to perform non-invasive comparative light reflection rheology on blood flow to the palms of the hands.
2. Background Art
Accurate and repeatable measurements of differential blood flow to the left and right arms are useful diagnostic indicators of overall cardiovascular conditions, and are used to determine the most helpful therapeutic treatments to improve the diagnosed cardiovascular conditions. For example, measurable differences in the radial pulses in the left and right arms are considered indicative of differential blood flow to the left and right arms.
According to the Erdman Therapy developed around 80 years ago by Frederick Erdman, there are two broad classes of circulatory types: (1) those who react to stress, disuse, trauma, and irritant substances by lowering the arterial tone, the tone of the smooth muscles of the arterial walls, and (2) those of a much larger class (probably 90-95% of the population) who react by increasing arterial tone, also known as vasomotor tone.
For example, a very stressful situation may cause some individuals to feel faint while others become agitated. The reactions are neurologically mediated and result in the first instance (faintness) in profound vessel dilation, and, in the second instance (agitation) in vessel constriction. The medical treatments appropriate for anxiety-induced faintness as opposed to anxiety-induced agitation are quite different.
Patients who have low vasomotor tone live to some degree in a perpetual faint, which they may or may not perceive, and these patients are likely to fare poorly on conventional medical therapies because these conventional therapies inadvertently may have vasodilating effects. One of the reasons this subset of patients is overlooked is that they comprise only a small minority of the population.
A fundamental objective of the Erdman Therapy is to improve the rate of blood flow for both classes of circulatory types. The majority of people who fall into the "normal" circulatory class in which their arteries become too constricted because the tone of the smooth muscles of their arterial walls is excessive find that their condition may be relieved through the use of heat, massage, and ultrasound therapies. All of these procedures and many medicines tend to reduce arterial tone, thereby improving the rate of blood flow in the majority of people.
Frederick Erdman's primary contribution was recognizing that the remaining minority of the population fall into a circulatory condition where at least some of their arteries are too dilated because their vasomotor tone is below normal. In this case, the indicated treatment is exactly opposite to that for the former group: namely, cold applications are required on the spinal muscles or at least portions thereof.
The most frequent medical syndrome in which low vasomotor tone is a major component is orthostatic hypotension associated with sensitivity to heat and fatigue from prolonged standing. Multiple sclerosis, severe chronic headache syndromes including migraines, insulin-dependent diabetes, hypoglycemia, hay fever or other allergies, and hyperactivity in children are all associated with this low vasomotor tone condition. Many juvenile asthmatics are also in this category.
Even though the great majority of the population fall into the first group which benefit from heat and massage and ultrasound treatments applied to the back, Erdman Therapy is uniquely capable of benefitting patients who are initially in the second group and require cold on the spine. By following a carefully monitored program of cold applications, patients can be transformed from the group requiting cold to the normal circulatory condition. Alternatively, those who are initially in the first group follow a program of gentle massage and warming type treatment applied to the back muscles to reduce excessive arterial tone. By recognizing the existence of these two diametrically opposed groups and applying appropriate treatment to each, the circulation and blood pressure of both groups can be improved.
Traditionally, the Erdman Therapy uses highly trained professionals to perform manual palpitation of the radial pulses to evaluate vasomotor tone, manually sensing the shape and amplitude of the pulse, a procedure devised to determine how to categorize a patient. The Yellow Emperor of China emphasized the importance of the radial pulse in his medical treatise of circa 2700 B.C., but Western medicine has not given much attention to pulse analysis, even though occasionally physicians have casually observed that the two radial pulses of an individual can often be quite different. Usually it is assumed that this condition of differing radial pulses is an anatomical variation rather than a variable physiological condition. While the radial pulses are both physiologically under the control of the central nervous system, they are, in particular, supplied by different sets of paraspinal ganglia. It appears that the afferent fibers supplying those ganglia for the right and left limbs do not symmetrically arise from the same sites, especially within the splanchnic (visceral) circulation. This is important because it may explain why patients with low vasomotor tone have gastrointestinal symptoms, as well as peripheral symptoms, and that both types of symptoms resolve when proper tone is restored.
The hallmark of patients who suffer from low vasomotor tone is a strong left pulse, especially after a gentle challenge of the appropriate spinal nerves with cooling. Pulse strength is characterized by pulse volume, pulse amplitude, and perceptible "push-through". Persons with low vasomotor tone can be treated by gentle intermittent applications of a cooling agent on the paraspinal nerve reflexes until the right pulse becomes dominant and both pulses have improved in tone. By carrying out the indicated therapies to correct each type of imbalance, a patient's circulatory condition can be restored to an optimum condition and symptoms can be reduced or alleviated, often dramatically.
Previous attempts to develop a method and apparatus to categorize non-invasively the vasomotor tone of patients without using manual palpitation of the radial pulses have not been successful. In the past, electromechanical radial pulse detectors have not proven to be adequately accurate and are not sensitive enough to monitor reliably the differential blood flow to the left and right arms. Blood flowmeter measurements made with various types of plethysmographs, ultrasound devices, electromagnetic devices, and nuclear magnetic resonance (NMR) flow imaging techniques are also insufficiently accurate.
Non-invasive monitoring of physiological conditions, particularly cardiovascular conditions, is known:
For example, U.S. Pat. No. 3,602,213 to Howell et at. discloses an apparatus and method for photoelectric dermachromography, employed for indicating the flow of blood in the capillary or arterial bed of the skin, and also for producing fine-grained examinations of the pulsations of the blood in the arterial and capillary systems. The Howell et al. apparatus graphically indicates and records, by electronic means, the differential blood flow to the skin in various related body areas. When such differential blood flow exists, this fact indicates to the examining physician or technician that one or more obstructions are present in the arterial system, and the location of such obstructions is determinable from the position at which the apparatus is applied to the skin of the patient and by isolation of arterial branches by manual occlusion of adjacent branches by pressure. The Howell et al. instrumentation and methods by which the relative blood flow to different areas of the skin may be detected and then visibly indicated and recorded do not require the exercise of any unusual skills, substantially eliminating the human error element in using the apparatus so that, with practice, a technician may use the apparatus satisfactorily without requiring the services of a physician. In particular, the Howell et at. patent discloses a method and apparatus for detecting occlusions in one of the internal carotid arteries by the differential sensing of epidermal blood flow in the supraorbital areas. A pair of photoelectric transducers that sense the relative absorption or reflection of light by the blood at the surface of the skin as an indication of blood flow are positioned over the supraorbital notches above the eyes. The sensor outputs are compared, and any unbalance indicates an occlusion in one of the carotid arteries.
U.S. Pat. No. 4,494,550 to Blazek et al. discloses quantitative evaluation of peripheral venous drainage disorders and arterial blood flow disorders in man, objectively detecting changes in cutaneous circulation under physical strain, and detecting obstacles to venous flow in the extremities. A plurality of radiation sources are directed onto the skin of the area of the respective extremity, and a radiation receiver measures the amount of radiation reflected or dispersed back by the cutaneous vascular plexus, and a temperature sensor simultaneously measures the skin temperature. An electronic evaluation circuit detects and records the progress of the reflected or dispersed amount of radiation and the skin temperature as a function of time. The simultaneous attachment of two or more Blazek et al. measuring heads to the electronic evaluation circuitry of the measuring apparatus enables the determination of the differences in measured values between normally supplied and poorly supplied areas of the skin.
U.S. Pat. No. 4,788,982 to Gedeon et al. discloses a device for determining the depth of anaesthesia of a patient including optical measuring means for measuring on a part of the patient an optical parameter such as the light reflected from this part of the patient. The light reflection is influenced by the circulation of the blood through this part of the patient's body, and produces an electric signal varying in accordance with this optical parameter. This signal is related to the periodic variations in the blood pressure of the patient with a frequency coinciding with the patient's heart frequency. The degree of anaesthesia of the patient can be correlated with the blood pressure variations and heart frequency extracted from the electric signal.
Both the Howell et al. and the Blazek et al. patents disclose differential sensing of blood flow using a pair of transducers that sense the relative absorption or reflection of light by epidermal blood in the respective body areas. However, both the Howell et al. and the Blazek et al. transducers disclose exposing relatively small areas of skin to the light, whereas the need exists for a device that exposes much larger areas of skin (for example, the skin of the palms) to the light. The Blazek et al. transducers preferably are also equipped with lenses giving a small aperture so that the emitted selective optical radiation can penetrate deep into the skin. The need exists, however, for a device that does not necessarily require the light transducers to be equipped with lenses.
Furthermore, as applied to the differential sensing of blood flow to the supraorbital areas, the Howell et al. patent requires that enough pressure is applied to the areas measured to eliminate the blood contributions to these areas from the superficial temporal, angular, and occipital arteries, leaving the internal carotid arteries as the only suppliers. The need exists, however, for a device that determines overall vasomotor tone without requiring the application of any such compression since the total blood flow to each hand is one object of the measurements using such a vasomotor tone sensor, not the detection of the individual contributions of particular arteries.
The Blazek et at. patent requires each transducer also to measure the temperature of the respective body area, and the plurality of sources of radiation are required to effect homogeneous cutaneous transillumination without subjecting the skin to elevated temperatures. The need exists, however, for a vasomotor tone sensor that does not require measurement of the temperature of the illuminated body area, and does not place any restrictions on subjecting the skin to elevated temperatures, other than the restriction of not raising the temperatures beyond what would be comfortable to the patient.
Furthermore, the Howell et at. patent discloses differential sensing of blood flow in the respective body areas using a pair of transducers so that any unbalance in the comparison of sensor output indicates an occlusion in one of the blood-supplying vessels, resulting perhaps from partial obstruction due to arteriosclerosis or thrombophlebitis. However, the Howell et at. apparatus and method for detecting such static and non-varying occlusions are unable to detect and repeatably indicate dynamic and variable physiological conditions such as overall vasomotor tone.
The Blazek et at. patent discloses recording the results of the light reflection rheology (LRR) procedure both before and after a change in the patient's physical position. In particular, the LRR curve is recorded when the measuring head is affixed to the inner side of the relaxed leg with the patient sitting with legs pendant. Then, the patient carries out a movement program, such as dorsal flexion of the ankle not more than 10 times in 15 seconds followed by letting the leg hang again in a relaxed resting state, causing the cutaneous vessels to empty, leading to changes in the cutaneous reflection that are also recorded. The need exists, however, for a vasomotor sensor that is not dependent on any transient emptying and/or refilling of the blood vessels. For example, a vasomotor sensor that measures the resting, steady-state LRR for both the left and right palms simultaneously when both arms are in a raised UP condition and again when both arms are in a lowered DOWN condition, would provide a better and more repeatable measurement of overall vasomotor tone.
The Gedeon et al. patent is representative of non-invasive LRR devices that can be used to monitor an overall passive and static physiological condition, for example, the degree or depth of anaesthesia of a patient. The need exists, on the other hand, for a method and apparatus that enables the use of non-invasive comparative LRR devices to monitor continuously an overall active and variable physiological condition, for example, the vasomotor tone of a patient. Further, it would be most desirable for such a vasomotor sensor to be portable, light-weight, relatively inexpensive, and easy to use.